This invention relates in general to slip ring assemblies for electrothermal deicer systems in aircraft. More particularly, it relates to a monitor that indicates when an electrical brush, used in such systems, has worn.
It is common for aircraft propeller blades to carry electrical heating elements or boots for preventing the build-up of ice on the blades. See, for example, U.S. Pat. No. 5,020,741 to Ziegler et al. Electrical power is transmitted to these boots, mounted on the rotating blades, from the stationary portion of the propeller assembly. Concentric slip rings, attached to the spinner bulkhead or propeller hub, contact non-rotating electrical brushes, mounted on the stationary support (or journal) for the rotor. Each ring typically transmits the power to a pair of blade boots.
Due to the constant rotational rubbing of the rings (typically copper) against the brushes (typically carbon graphite), the brushes tend to wear. This occurs most at their ends ("end wear") but also can occur along their flanks ("flank wear").
Because of the tight fit between the rotating and stationary portions of the propeller assembly, the brushes are basically unseen. It is virtually impossible to detect, strictly through visual checking, when the brushes start to wear and are about to become inoperative.
Accordingly, it is the primary object of the present invention to provide a warning system that indicates electrical brush wear.
It is another object to provide a detection system that automatically indicates when the amount of wear is excessive and necessitates brush replacement.
It is another object to provide a detection system that automatically indicates excessive end wear and/or flank wear.
It is another object to provide a brush-wear indicator that is extremely simple, yet highly reliable.
The above and other objects will become more readily apparent when the following description is read in conjunction with the accompanying drawings.